Sailors normally wear rubber boots beneath trousers made of waterproof material, generally cloth coated with water-proofing or "oilskins", thereby preventing water that is running down the trouser legs from penetrating into the boots. However, this technique is not satisfactory when working on deck while the sea is rough since waves breaking over the sailor's feet rise up the boot. Indeed, the curved front shape of a boot facilitates the passage of water between the boot upper and the trouser leg so that the water penetrates into the boot. In an attempt to keep their feet dry, sailors tend to turn their backs to the waves while they are maneuvering, but this is not always possible.
Tests have shown that changing the curved front shape of the boot to form a "breakwater" does not suffice, while sealing the oilskin trouser legs to the boots gives rise to an assembly that is rather rigid and does not allow the necessary freedom of movement.
A similar problem arises in some kinds of winter sports (e.g. snow scooter driving), where snow kicked up by the vehicle gets in between the trouser leg and the boot, and ends up by melting inside the boot.